Taxol is a naturally occurring compound which has shown great promise as an anti-cancer drug. For example, Taxol has been found to be an active agent against drug-refractory ovarian cancer by McGuire et al. See “Taxol: A Unique Anti-Neoplastic Agent With Significant Activity Against Advanced Ovarian Epithelial Neoplasms.” Ann. Int. Med., 111, 273-279 (1989). All patents, scientific articles, and other documents mentioned herein are incorporated by reference as if reproduced in full below.
Unfortunately, Taxol has extremely low solubility in water, which makes it difficult to provide a suitable dosage form. In fact, in Phase I clinical trials, severe allergic reactions were caused by the emulsifiers administered in conjunction with Taxol to compensate for Taxol's low water solubility; at least one patient's death was caused by an allergic reaction induced by the emulsifiers. Dose limiting toxicities include neutropenia, peripheral neuropathy, and hypersensitivity reactions.
Brown et al., in “A Phase I Trial of Taxol Given by A 6-Hour Intravenous Infusion” J of Clin Oncol, Vol. 9 No. 7, pp. 1261-1267 (July 1991) report on a Phase I Trial in which Taxol was provided as a 6-hour IV infusion every 21 days without premedication. 31 patients received 64 assessable courses of Taxol. One patient had a severe (or acute) hypersensitivity reaction, which required discontinuation of the infusion and immediate treatment to save the patient's life. Another patient experienced a hypersensitivity reaction, but it was not so severe as to require discontinuing the infusion. Myelosuppression was dose-limiting, with 2 fatalities due to sepsis. Non-hematologic toxicity was of Grade 1 and 2, except for one patient with Grade 3 mucositis and 2 patients with Grade 3 neuropathy. The neuropathy consisted of reversible painful paresthesias, requiring discontinuation of Taxol in two patients. Four partial responses were seen (3 in patients with non-small-cell lung cancer, and one in a patient with adenocarcinoma of unknown primary). The maximum tolerated dose reported was 275 mg/m2, and the recommended Phase II starting dose was 225 mg/m2. The incidence of hypersensitivity reaction was reported to be schedule-dependent, with 6 to 24-hour infusions of drug having a 0% to 8% incidence of hypersensitivity reactions. It was also reported that hypersensitivity reactions persist with or without premedication despite prolongation of infusion times. Since these Phase I studies were conducted on terminally ill patients suffering from a variety of cancers, the efficacy of the Taxol treatments could not be determined.
In a study by Kris et al., Taxol formulated with Cremaphor EL in dehydrated alcohol was given as a 3-hour IV infusion every 21 days, with the administered dosage ranging from 15 to 230 mg/m2 in nine escalation steps. Kris et al. concluded that “with the severity and unpredictability of the hypersensitivity reactions, further usage of Taxol is not indicated with this drug formulation on this administration schedule.” See Cancer Treat. Rep., Vol. 70, No. 5, May 1986.
Since early trials using a bolus injection or short (1-3 hour) infusions induced anaphylactic reactions or other hypersensitivity responses, further studies were carried out in which Taxol was administered only after premedication with steroids (such as dexamethasone), antihistamines (such as diphenhydramine), and H2-antagonists (such as cimetidine or ranitidine), and the infusion time was extended to 24 hours in an attempt to eliminate the most serious allergic reactions. Various Phase I and Phase II study results have been published utilizing 24-hour infusions of Taxol with maximum total dosages of 250 mg/m2, generally with the course being repeated every 3 weeks. Patients were pre-treated with dexamethasone, diphenhydramine, and cimetidine to offset allergic reactions. See Einzig, et al., “Phase II Trial of Taxol in Patients with Metastatic Renal Cell Carcinoma,” Cancer Investigation, 9(2) 133-136 (1991), and A. B. Miller et al., “Reporting Results of Cancer Treatment,” Cancer, Vol 47, 207-214 (1981).
Koeller et al., in “A Phase I Pharmacokinetic Study of Taxol Given By a Prolonged Infusion Without Premedication,” Proceedings of ASCO, Vol. 8 (March, 1989), recommends routine premedication in order to avoid the significant number of allergic reactions believed to be caused by the cremophor (polyethoxylated castor oil) vehicle used for Taxol infusions. Patients received dosages ranging from 175 mg/m2 to 275 mg/m2.
Wiernik et al. in “Phase I Clinical and Pharmacokinetic Study of Taxol,” Cancer Research, 47, 2486-2493 (May 1, 1987), also report the administration of Taxol in a cremophor vehicle by IV infusion over a 6-hour period in a Phase I study. Grade 3-4 hypersensitivity reactions incurred in 4 of 13 courses. The starting dose for the study was 15 mg/m2 (one-third of the lowest toxic dose in dogs). Doses were escalated, and a minimum of 3 patients were treated at each dose level until toxicity was identified, and then 4-6 patients were treated at each subsequent level. The study concluded that neurotoxicity and leukopenia were dose-limiting, and the recommended Phase II trial dose was 250 mg/m2 with premedication.
Other exemplary studies on Taxol include: Legha et al., “Phase II Trial of Taxol in Metastatic Melanoma,” Vol. 65 (June 1990) pp. 2478-2481; Rowinsky et al., “Phase I and Pharmacodynamic Study of Taxol in Refractory Acute Leukemias,” Cancer Research, 49, 4640-4647 (Aug. 15, 1989); Grem et al., “Phase I Study of Taxol Administered as a Short IV Infusion Daily For 5 Days,” Cancer Treatment Reports, Vol. 71 No. 12, (December, 1987); Donehower et al., “Phase I Trial of Taxol in Patients With Advanced Cancer,” Cancer Treatment Reports, Vol. 71, No. 12, (December, 1987); Holmes et al., “Phase II Study of Taxol in Patients (PT) with Metastatic Breast Cancer (MBC),” Proceedings of the American Society of Clinical Oncology, Vol. 10, (March, 1991), pp. 60. See also Suffness. “Development of Antitumor Natural Products at the National Cancer Institute,” Gann Monograph or Cancer Research, 31 (1989) pp. 21-44 (which recommends that Taxol only be given as a 24-hour infusion).
Weiss et al., in “Hypersensitivity Reactions from Taxol,” Journal of Clinical Oncology, Vol. 8, No. 7 (July 1990) pp. 1263-1268, reported that it was difficult to determine a reliable overall incidence of hypersensitivity reactions, HSRs, because of the wide variations in Taxol doses and schedules used, and the unknown degree of influence that changing the infusion schedule and using premedication has on HSR incidents. For example, of five patients who received Taxol in a 3-hour infusion at greater than 190 mg/m2 with no premedication, three had reactions, while only one out of 30 patients administered even higher doses over a 6-hour infusion with no premedication had a reaction. Therefore, this suggests that prolonging the infusion to beyond 6 hours is sufficient to reduce HSR incidents. Nevertheless, Weiss et al. found that patients receiving 250 mg/m2 of Taxol administered via a 24-hour infusion still had definite HSRs. Thus, while prolonging drug infusion to 6 or 24-hours may reduce the risk for an acute reaction, this conclusion can not be confirmed, since 78% of the HSR reactions occurred within ten minutes of initiating the Taxol infusion, which indicates that the length of time planned for the total infusion would have no bearing. Further, concentration of Taxol in the infusion may also not make a difference since substantial numbers of patients had reactions to various small Taxol dosages. Finally, not only is the mechanism of Taxol HSR unknown, it is also not clear whether Taxol itself is inducing HSRs, or if the HSRs are due to the excipient (Cremaphor EL; Badische Anilin und Soda Fabrik AG [BASF], Ludwigshafen, Federal Republic of Germany). Despite the uncertainty as to whether or not premedication had any influence on reducing the severity or number of HSRs, prophylactic therapy was recommended, since there is no known danger from its use.
The conflicting recommendations in the prior art concerning whether premedication should be used to avoid hypersensitivity reactions when using prolonged infusion durations, and the lack of efficacy data for infusions done over a six-hour period has led to the use of a 24-hour infusion of high doses (above 170 mg/m2) of Taxol in a Cremaphor EL emulsion as an accepted cancer treatment protocol.
Although it appears possible to minimize the side effects of administering Taxol in an emulsion by use of a long infusion duration, the long infusion duration is inconvenient for patients, and is expensive due to the need to monitor the patients for the entire 6 to 24-hour infusion duration. Further, the long infusion duration requires that patients spend at least one night in a hospital or treatment clinic.
Higher doses of paclitaxel have also been described in the literature. To determine the maximal-tolerated dose (MTD) of paclitaxel in combination with high-dose cyclophosphamide and cisplatin followed by autologous hematopoietic progenitor-cell support (AHPCS), Stemmer et al (Stemmer S M, Cagnoni P J, Shpall E J, et al: High-dose paclitaxel, cyclophosphamide, and cisplatin with autologous hematopoietic progenitor-cell support: A phase I trial. J Clin Oncol 14:1463-1472, 1996) have conducted a phase I trial in forty-nine patients with poor-prognosis breast cancer, non-Hodgkin's lymphoma (NHL) or ovarian cancer with escalating doses of paclitaxel infused over 24 hours, followed by cyclophosphamide (5,625 mg/m2) and cisplatin (165 mg/m2) and AHPCS. Dose-limiting toxicity was encountered in two patients at 825 mg/m2 of paclitaxel; one patient died of multi-organ failure and the other developed grade 3 respiratory, CNS, and renal toxicity, which resolved. Grade 3 polyneuropathy and grade 4 CNS toxicity were also observed. The MTD of this combination was determined to be paclitaxel (775 mg/m2), cyclophosphamide (5,625 mg/m2), and cisplatin (165 mg/m2) followed by AHPCS. Sensory polyneuropathy and mucositis were prominent toxicities, but both were reversible and tolerable. Eighteen of 33 patients (54%) with breast cancer achieved a partial response. Responses were also observed in patients with NHL (four of five patients) and ovarian cancer (two of two patients).
U.S. Pat. No. 5,641,803 reports the use of Taxol at doses 175 and 135 mg/m2 administered in a 3 hour infusion. The infusion protocols require the use premedication and reports the incidences of hypersensitivity reactions in 35% of the patients. Neurotoxicity was reported in 51% of patients with 66% of patients experiencing neurotoxicity in the high dose group and 37% in the low dose group. Furthermore, it was noted that 48% of patients experienced neurotoxicity for longer infusion times of 24 hours while 54% of patients experienced neurotoxicity for the shorter 3 hour infusion.
There is evidence in the literature that higher doses of paclitaxel result in a higher response rate. The optimal doses and schedules for paclitaxel are still under investigation. To assess the possibility that paclitaxel dose intensity may be important in the induction of disease response, Reed et al of NCI (Reed E, Bitton R, Sarosy G, Kohn E: Paclitaxel dose intensity. Journal of Infusional Chemotherapy 6:59-63, 1996) analyzed the available phase II trial data in the treatment of ovarian cancer and breast cancer. Their results suggest that the relationship between objective disease response and paclitaxel dose intensity in recurrent ovarian cancer is highly statistically significant with two-side p value of 0.022. The relationship in breast cancer is even stronger, with a two-sided p value of 0.004. At 135 mg/m2/21 days, the objective response rate was 13.2%; and at 250 mg/m2/21 days, the objective response rate was 35.9%. The response rate seen at the intermediate dose of 175 mg/m2 was linear with the 135 mg/m2 and 250 mg/m2 results and the linear regression analysis shows a correlation coefficient for these data of 0.946 (Reed et al, 1996).
In a study by Holmes (Holmes F A, Walters R S, Theriault R L, et al: Phase II trial of Taxol, an active drug in the treatment of metastatic breast cancer. J Natl Cancer Inst 83:1797-1805, 1991), and at MSKCC (Reichman B S, Seidman A D, Crown J P A, et al: Paclitaxel and recombinant human granulocyte colony-stimulating factor as initial chemotherapy for metastatic breast cancer. J Clin Oncol 11:1943-1951, 1993), it was shown that higher doses of TAXOL up to 250 mg/m2 produced greater responses (60%) than the 175 mg/m2 dose (26%) currently approved for TAXOL. These results however, have not been reproduced due to higher toxicity at these higher doses. These studies, however, bear proof to the potential increase in response rate at increased doses of paclitaxel.
Since premedication is required for Taxol, that often necessitates overnight stays of the patient at the hospital, it is highly desirable to develop a formulation of paclitaxel that obviates the need for premedication.
Since premedication is required for Taxol, due to HSR's associated with administration of the drug, it is highly desirable to develop a formulation of paclitaxel that does not cause hypersensitivity reactions. It is also desirable to develop a formulation of paclitaxel that does not cause neurotoxicity.
Since Taxol infusions are generally preceded by premedication, and require post-infusion monitoring and record keeping, that often necessitates overnight stays of the patient at the hospital, it is highly desirable to develop a formulation of paclitaxel which would allow for recipients to be treated on an out-patient basis.
Since it has been demonstrated that higher doses of Taxol achieve improved clinical responses albeit with higher toxicity, it is desirable to develop a formulation of paclitaxel which can achieve these doses without this toxicity.
Since it has been demonstrated that the dose limiting toxicity of Taxol is cerebral and neurotoxicity, it is desirable to develop a formulation of paclitaxel that decreases such toxicity.
It is also desirable to eliminate premedication since this increases patient discomfort and increases the expense and duration of treatment.
It is also desirable to shorten the duration of infusion of Taxol, currently administered in 3 hours-24 hours to minimize patient stay at the hospital or clinic.
Since Taxol is currently approved for administration at concentrations between 0.6-1.2 mg/ml and a typical dose in humans is about 250-350 mg, this results in infusion volumes typically greater than 300 ml. It is desirable to reduce these infusion volumes, by developing formulations of paclitaxel that are stable at higher concentrations so as to reduce the time of administration.
Since infusion of Taxol is limited to the use of special I.V. tubing and bags or bottles due to the leaching of plasticizers by the cremaphor in the Taxol formulaton, it is desirable to develop a formulation of paclitaxel that does not have cremaphor and does not leach potentially toxic materials from the conventionally used plastic tubings or bags used for intravenous infusion.